The invention relates to a method and a device for supplying a compressor with compressed air in an internal combustion engine.
Internal combustion engines of this type, for example piston engines, such as diesel engines, have a compressor for generating compressed air which is required for various purposes, for example for a compressed air brake system or an auxiliary air cell for various intended uses.
The applicant is aware of a compressor which is fed with air from the intake manifold of the internal combustion engine. Depending on the operating state and the rotational speed of the engine supercharged, for example, by a turbocharger, the pressure at the extraction point from the intake manifold is higher than the ambient air. The compressor consequently changes its operation from straightforward suction operation to supercharged operation, markedly increasing its efficiency and therefore the air quality conveyed. This arrangement has the disadvantage that the compressor extracts pressure-loaded air from the intake manifold and consequently withholds it from the internal combustion engine. That is to say, the power of the internal combustion engine in this operating state is reduced, in turn, by the discharged air, this being undesirable.
The object of the present invention, therefore, is to provide a method and a device for supplying a compressor with compressed air in an internal combustion engine, the above disadvantages being eliminated or significantly reduced, and further advantages being afforded.
A basic idea of the invention is that a point for the extraction of air for the compressor is arranged at a point on the internal combustion engine located at its exhaust manifold.
What is advantageously achieved thereby is that the intake air quantity for the internal combustion engine is not decimated, therefore its power is not restricted.
In modern internal combustion engines with an electronically controlled fuel supply operating in overrun, fuel is no longer supplied, in order thereby to reduce the energy consumption of the internal combustion engine in this operating state. It is used, in overrun, only for generating compressed air, that is to say the intake air is compressed in the cylinders and is blown out into the exhaust manifold and the exhaust line. This compressed exhaust air is built up and compressed by a throttle device, so that it has a markedly higher pressure level than the ambient air. This throttle device may be, for example, a conventional engine brake flap of an engine brake system already present, the said engine brake flap reducing or even shutting off the cross section of the exhaust line. The air thus highly compressed is then extracted via a controlled extraction valve from the exhaust manifold or the exhaust line and is supplied to the compressor which is thereby operated as a supercharged compressor with increased efficiency.
The internal combustion engine has an engine control apparatus for fuel supply which obtains operating parameters from sensors often already present in the vehicle. These data are in many cases also available on a vehicle bus system, for example a CAN bus. A control unit takes over these data in order to determine the operating states and can consequently control the extraction valve and the throttle device at the correct timepoint such that the compressed air generated by the cylinders in overrun and built up by the throttle device is supplied to the compressor. The valve may even be connected only in the case of one cylinder and/or in the case of all cylinders in order to acquire the possibility of a broad variation of compressed-air generation quantities.
With a comparable pressure level, the compressed air thus obtained is hotter than the compressed air which is extracted from the intake manifold, since it is likewise heated up by the engine which is heated during combustion. The efficiency of the compressor supercharged by the compressed air is therefore not as high as when the air comes from the intake manifold, although this air is also often preheated. When the internal combustion engine is in overrun, however, there is excess energy, and in this case the lowered efficiency of the compressor is negligible.
In a further version, the compressed air extracted from the exhaust line may be cooled by a heat exchanger.
Furthermore, the inlet of the compressor may be connected to the atmosphere via an inlet valve controllable by the control unit, so that, even when the internal combustion engine is in combustion mode, air can be compressed during normal operation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings.